Medium-sized larva. up to 8 mm long. Head yellowish brown; body pale brownish. Head capsule slender; cephalic index about 0.6. Dorsally DP absent; dorsal setal sockets in straight line, S5 and S8 posteromesial to S7. Ventrally S9-S10-SSm forming near straight to gently curved line; VP oval, bigger than setal sockets, unaligned. Setae undescribed and not visible.
Half head length, 3x as long as mandible. Antennal ratio 2.5-2.8. Basal segment 10x as long as basal width, with ring organ at 0.4; segment 2 11x as long as wide, with slight swelling on basal, outer margin; segment 3 4x as long as wide, larger than last segment by 1 segment width; last segment a slender peg. Style swollen in distal 1/2, extending beyond middle of last segment, with 2 strongly sclerotized rings in basal 1/2. Peg sensilla about as long as last segment, forming a process similar to a tuning fork. Blade about as long as segment 2; basal ring about 3 x as high as wide. Accessory blade as long as flagellum.
Gradually curved, strongly narrowed in apical 1/2. Apical tooth 3x as long as basal width, 1/3 length of mandible. Inner tooth moderately developed, overlapping strong seta subdentalis; mola hardly dilate. Ventrolateral setae simple, in close row on outer margin of proximal 1/3 of mandible; seta 1 not discernible; gap between ring organ and seta 3 2x as great as that between setae 2 and 3.
Basal segment of palp about 4x as long as wide; ring organ at 0.6.
Without fringe of swim-setae. Anal tubules slender, spindle-shaped, 6x as long as wide, not quite 1/2 as long as posterior parapod. Procercus pale, 3.5x as long as wide, with 7 pale apical setae. Claws of posterior parapod simple; some larger claws with a few small, very fine points on inner and/or outer margin; some smaller claws with narrow, lamellate outer margin, sometimes also inner ones lamellate in basal 1/2.
Pentaneurella belongs to the Pentaneurini, but seems related neither to Pentaneura or Trissopelopia which it resembles as adult. In contrast to Pentaneura and Trissopelopia, the peg sensilla of Pentaneurella are large and placed as though firmly fused with the margin of antennal segment 2, in a tuning fork-like process. The ligula with middle tooth recessed and inner teeth curved outward resembles that of Krenopelopia, but the absence of a dorsal pit separates Pentaneurella from this genus.
Larvae of the only currently known species (P. katterjokki) were found by Thienemann in springs and spring-fed streams in Swedish Lappland, and by Murray in a mountain stream in northern Norway.